1. FIELD OF INVENTION
This invention relates to electronic control of evaporative coolers and is particularly directed to automatic means for controlling the operation of the pump and blower of an evaporative cooler, air conditioner or the like.
2. PRIOR ART
Evaporative coolers have been in use for many years as a relatively low-cost means of cooling residential and commercial buildings. As is well known, these devices comprise a pump for pumping water to permeate one or more porous pads, together with a one or two speed fan or blower for pulling air through the pads and delivering the air into the building. As the air is pulled through the water-soaked pads, the water is caused to evaporate which reduces the temperature of the air and the cooled air is then blown into the building to provide cooling. Generally, evaporative coolers require a; one switch for turning the water pump on and off and a second or combined switch for controlling the blower speeds. Furthermore, unless the water pump is turned on approximately five minutes prior to turning on the blower, unpleasant odors may be blown into the building along with blasts of hot air. This is the reason that evaporative coolers are often referred to, colloquially, as "swamp coolers".
Evaporative coolers are considerably less expensive to operate than air conditioners and, in regions of low humidity, such as the southwestern states, they are quite effective. However, as humidity increases, the efficiency of evaporative coolers decreases rapidly. Consequently, in some areas, it is necessary to combine both forms of cooling to obtain the advantages under the appropriate conditions.
Air conditioners are designed to operate in an ON-OFF cycle, controlled by a separate thermostat, to provide the desired cooling without requiring manual operation to turn the unit on and off. Furthermore, air conditioners operate by refrigerating the air and, hence, can reduce the air temperature rapidly to below the desired temperature and, thereafter, can cycle on and off to maintain an approximation of the desired temperature. For this purpose, temperature sensing mechanisms, such bi-metal thermostats, having an on-off differential of as about three degrees Fahrenheit are necessary. In recent years, attempts have been made to provide automatic controls for evaporative coolers. However, this presents very different problems than with air conditioners.
The requirements for such a system are herein listed: